The present invention relates generally to electrical device testing, and more particularly to a two-axis self-centering floating probe block assembly for testing an electrical device.
Electrical testing of electrical devices often involves insertion probing of a receptacle of the device. For example, a cellular phone often includes a receptacle configured as an array of signal points on the device under test (hereinafter referred to as the xe2x80x9csystem connectorxe2x80x9d). The device, in this example a cellular phone, may also include alternatively configured receptacles such as an audio receptacle into which a headset audio plug is inserted or a charger receptacle into which an A/C charger plug is inserted to charge up the device.
During or after manufacturing, various tests are performed on the device (hereinafter referred to as xe2x80x9cdevice under testxe2x80x9d or xe2x80x9cDUTxe2x80x9d). Typically at least one or more tests require insertion probing of one or more of the DUT receptacles. Insertion probing involves the insertion of a probe into a mating DUT receptacle such that the probe and DUT receptacle make electrical contact. The electrical contact is the means through which the probe stimulates and/or receives measurement signals from the DUT. Although insertion probing is itself a conceptually straightforward idea, the design of the probe that is used for this purpose does require several important considerations. First, due to manufacturing limitations, at least some error relative to specification typically exists in the precision of the location of the electrical pads of the device which the probe must electrically contact. Thus, over hundreds and thousands of a given device to be tested, the probe must be designed to take into account the pad location tolerances such that it can reliably make electrical contact with each DUT to be probed.
In order to account for the pad location tolerances of a given DUT design, a xe2x80x9cfloatingxe2x80x9d probe block is sometimes used. In a floating probe block, the probe is attached to a block which is encased in substantially conforming frame that holds the block in place while allowing the block a small amount of xe2x80x9cwiggle roomxe2x80x9d within the frame. This solution allows the receptacle itself to assist in aligning the probe within the receptacle. However, this design is not ideal because since the average center position of the DUT receptacle from DUT to DUT is not necessarily aligned with the average resting position of the probe block within its frame, gravity and cable forces tend to bias the probe block to its lowest position within the frame. This increases probing force and wear on the bottom of the probe block. This also limits the probing variance range allowed by the probe.
Another prior solution is to mount the probe block on two non-floating pins. These pins pass through clearance holes in the probe block, and the sizing of the holes is the means by which the float is constrained. These holes are typically formed with a triangular cross-section so that when gravity pulls on the probe block, the holes operate to center the probe block on the pins. This design is also not ideal because the probe block is centered only horizontally (left-to-right) and not vertically (up and down). Accordingly, oftentimes the gravitational force on the block is insufficient for centering the block against cable forces. In addition, this arrangement does not allow for full circular float of the probe block.
Another prior solution involves constraining the float with the outside profile of the probe block. In the float gap, Poron(copyright) or some other foam-like material is placed to bias the probe block to the center. This design is also not ideal because the foam can take on a compression set and therefore perform poorly. Additionally, the centering force increases relatively quickly with respect to the distance the probe block is from the center, again increasing wear.
The present invention is a two-axis self-centering probe block assembly with two-axis float and self-alignment. The invention uniquely provides a floating probe block assembly whose average disengaged position is directly aligned with the average DUT-to-DUT position of the mating receptacle when looking through a plane perpendicular to the probing direction. Additionally, the design of the probe is such that very little force is required by the probe actuator to cause the probe block to self-align. This increases reliability of probing multiple ways. The total amount of float is therefore greater than that achievable in prior art solutions, and the probe block is subject to decreased wear since less friction is involved in self-aligning.
The invention is ideal for use in a test fixture during manufacturing test of a printed circuit board or final-level test of a device under test (DUT) in which the DUT requires some insertion probing of a receptacle. The invention compensates for DUT-to-DUT and fixture-to-fixture differences over thousands of DUTs, in a novel manner that is more reliable than other methods currently used.